1. Field of the Invention
A shieldable blood collection needle assembly with a flashback chamber for providing confirmation of venous entry.
2. Description of Related Art
Needle assemblies are used for collecting specimens of fluid, such as blood, from a patient. Some such needle assemblies are intended for use with an evacuated tube, such as tubes sold under the trademark VACUTAINER™ by Becton, Dickinson and Company. Needle assemblies for use with an evacuated fluid collection tube include a needle hub with a proximal end, a distal end and a passage extending between the ends. The needle assembly further includes at least one needle cannula mounted to the needle hub. The needle cannula includes a sharply pointed distal end that projects distally beyond the needle hub, a proximal end that projects proximally beyond the needle hub and a lumen that provides communication between the opposed ends of the needle cannula. Some needle assemblies include separate proximal and distal cannulas and rely upon a portion of the needle hub to provide communication between the lumens of the respective cannulas. The distal end of the needle cannula typically is beveled to a tip that is sufficiently sharp for piercing the skin of the patient and accessing the vein or other source of fluid that is to be collected. The proximal end of the needle cannula is configured for piercing the rubber stopper on an evacuated tube. The proximal end of the needle cannula typically is covered by a needle pierceable resealable multi-sample sleeve. The sleeve is compressed by the rubber stopper of the evacuated tube and punctured by the proximal end of the needle cannula as the proximal end of the needle cannula is urged into communication with the evacuated tube.
One problem with collecting fluid from a patient relates to uncertainty during attempts to access the proper source of fluid in the patient. For example, a blood collection procedure typically requires the phlebotomist to visually locate a vein and then to enter the vein with the distal end of the needle cannula. The phlebotomist may not have a positive indication of venous entry at this stage. An evacuated tube then is placed in communication with the proximal end of the needle cannula once the phlebotomist is reasonably certain that the targeted blood vessel has been entered. The low pressure within the evacuated tube then cooperates with the higher pressure of the blood to generate a flow of blood into the tube. The flow of blood into the tube may be the first positive indication to the phlebotomist that the targeted blood vessel has been accessed. The initial flow of blood along the long needle cannula and into the evacuated tube may take a relatively long time based on several factors, including the relative pressure levels and the length and cross-sectional dimensions of the needle cannula. The phlebotomist may interpret the absence of an immediate flow of blood as being a sign that the blood vessel was not targeted properly, when in fact the absence of a visible blood flow in the evacuated tube may be attributable to pressure and fluid flow characteristics. Thus, the phlebotomist may unnecessarily withdraw the needle and start the blood collection procedure again. As a result, time is wasted and trauma for the patient is increased. In view of the above problems, many fluid collection needle assemblies are provided with a flashback chamber that communicates with the needle cannula. The flashback chamber typically is formed at least partly from a transparent or translucent material and is intended to receive a portion of the blood flow shortly after a vein has been accessed properly.
The blood collection needle assembly is withdrawn from the patient after a suitable number of samples have been collected. The used needle assembly then is discarded. The medical profession is well aware that accidental sticks with a used needle cannula can transmit disease. Accordingly, it is desirable to shield the used needle cannula immediately after the needle cannula has been withdrawn from the patient. Shields have taken many different forms. For example, some shields telescope in a distal to proximal direction over the needle cannula and frictionally engage the needle hub. Shields of this type create the risk of an accidental needle stick during shielding if the shield is misaligned with the needle cannula. Some shields of this general type are provided with enlarged collars that are intended to minimize the risk of accidental sticks during shielding. However, shields of this general type are not preferred. Other shields are telescoped over the needle hub and can be moved distally over the needle cannula to effect shielding. Shields of this general type are safe and effective and are used in many situations. However, shields of this type can interfere with the normal usage of some medical implements. Other shields are hingedly mounted to or near the needle hub and can be rotated from an open position where the needle cannula is exposed to a closed position where the needle cannula is shielded. Shields of this type also work very well and are widely accepted. However, the existence of a hinged shield on a fluid collection needle assembly with a flashback chamber is intuitively problematic in view of the complexities of providing both shielding and an unobstructed view of the flashback chamber.